The nFAULT pin signals a problem with the chip via an open-drain output. A motor fault, undervoltage condition, or TJ > 160°C drives the pin low. This output is not valid when nSLEEP puts the device into minimum power dissipation mode (that is, nSLEEP is low). nFAULT stays asserted (nFAULT = L) until VBB reaches VBBNFR to give the charge pump headroom to reach its undervoltage threshold. nFAULT is a status-only signal and does not affect any device functionality. The H-bridge portion still operates normally down to VBB = 8 V with nFAULT asserted.